2)There are various P/Ns (various OEMs) of Window Heat Controller Unit (WHCU) installed on B727/B737. All P/Ns are fully interchangeable.

P/N

Boeing P/N

OEM

231-2

Nil

Astronic

83000-05601 / -05602

10-61833-2

Koito

65-52803-8

Nil

BAE Systems

3)There were 4 units of WHCU installed on 727 (and B737) airplane which for pilot and co-pilot No. 1 and No. 2 windows. The WHCU located at E5-1 electrical rack. It consists of temp controller which a solid state device that performs overheat control and temp control, overheat relay which direct 115V AC power from window heat CB to temp controller when energized and transformer which provide high voltage for heating window.

B) Data

1)Repair and Findings Data from 1st Jan 2005 till 31st May 2008 were reviewed and has been classified into various types of common defect and shop findings; s/n and aircraft with repeated removals. Total 43 units were removed unscheduled with 30 DC and 13 DNC. None were scrapped or overhauled.

2) Comments from Astronics Advanced Eletronics Systems (previously known as General Dynamics or Olin or Pacific Electro Dynamics)

a)OEM does not track the MTBUR and MTBF of Window heat controller unit p/n 231-2.

b)231-5 is the latest WHCU p/n produce by Astronics. It is fully interchangeable with p/n 231-2 with an addition of BITE circuits.

c)Suspect the latest mods (Mod L or M depending on the age of the unit) have not been incorporated for serial number that have failures of parts in the output transistor section (Q26, 27, 28)

d)Astronics has produced 16 SBs related to WHCU p/n 231-2. Refer attachment 7B for modification history from p/n 231-1 to 231-2 mod ‘M’.

e)Astronics only do repair and re-certify origin WHCU p/n 231-x from astronics or all predecessor company names for astronics.

f)Astronics provide recommendation per below:

1.Due to cooling air system accumulates dust and dirt which creates thermal stress on the unit, operator is recommended to review the maintenance chk task to inspect the cooling system and cleaning the dust and dirt in E&E compartment to keep dust from clogging the units.

2.Operator to record mod level for each WHCU installed on the fleet.

3.Any units had RV1-4 or F1 changed should have Q1 changed as well or there is risk of recurrence of the problem.

3) Comments from Koito Mfg

a)Design MTBUR for WHCU p/n 83000-05602 is 14046 hrs.

b)Since most of the operators has already incorporated new WHCU p/n: 83000-05604, there is no news about p/n 83000-05602 recent few years.

c)P/n 83000-05604 has a BITE function while -05602 has not. The other differences are the weight of unit. -05604 weight is 4.3 kg while -05602 is 3.7 kg.

4) Comments from Aero Technology

a)No expected MTBUR and no recommended improved part number from repairer.

b)Other operators do not have low time failure (LTF) for window heat controller p/n 231-2.

c)Two units (S/n 478 & 6205) LTF was warranty denied.

1)S/n 478 was repaired at 1st time visit. Nil faults found for 2nd shop visit.

2)S/n 6205 found internal damaged due to excessive heat on Oct 07. 1 month later the unit was sent for repair and found different circuit board had failed. It appears that the second failure was also caused by an excessive heat.

d)Unable to offer exchange with upgraded p/n due to no stock available.

E) Findings and Discussion.

1)16 out of 43 WHCU unscheduled removals were caused by overheat. From the study, overheat will affect the window and cause the window to crack. 5 unscheduled removals due to CBs tripped can also cause window to overheat.

Reason for Removals

%age

Total

DC

DNC

Overheat / fail overheat test

37.2

16

13

3

Nil heating / inop

25.6

11

9

2

Nil control / nil indication / not regulating / not function

11.6

5

3

2

CB tripped

11.6

5

2

3

Window cracked / arching

9.3

4

1

3

Green light intermittent

4.7

2

2

0

Total

43

30

13

2)29 (67.4%) units were sent to Aero Tech for repair, 6 (14%) to Aero Instrument, Avborne 3, High Tech Avionic 1 and Aero Control Avionic and ST Aero 2 each. Most of units were sent to Aero Tech due to low flat rate compare to other vendor.

Aero Tech

Aero Instrument

Aero Control Avionic

Avborne

ST Aero

High Tech Avionics

Total

2005

4

1

2

3

2

-

12

2006

9

1

-

-

-

-

10

2007

15

4

-

-

-

-

19

2008

1

-

-

-

-

1

2

Total

29 (67.4%)

6 (14%)

2 (4.65%)

3 (7%)

2 (4.65%)

1 (2.3%)

43

3)Currently there were 57 units installed on the fleet which 47.4% was manufactured by Astronics, 33.3% by BAE system and 17.5% by Koito.

5)Most of the WHCU (47.4%) belongs to Astronic. However, Boeing has limited knowledge of the unit and cannot determine the replacement of part 231-2 with 231-5.

6)All of Astronics p/n 231-2 was not upgraded to latest mod L or M.

7)Koito unit is the most recommended p/n due to 50% of the unit is in good condition and only one was removed unscheduled for the last 1 year. Furthermore, Boeing only recognizes Koito p/n compared to Astronics or BAE p/n.

8)BAE p/n 65-52803-8 had shown only 5 units removed unscheduled last year (2007). Compared to Astronics and Koito, BAE WHCU reported fewer problems. However, the OEM (BAE) is NOT contactable.

F) Recommendations

1)To advice repairer; unit found with varistor (RV1-4) or fuse (F1) defect/damaged, transistor Q1 must be replaced to prevent from tripping and overheat shutdown

7)Inform the maint crew to follow the troubleshooting chart in AMM 30-41-02 figure 101 before make a decision to replace the WHCU due to failure. Ensure that the window temperatures are below 75°F and No. 2 windows are closed and latched before using the troubleshooting chart.

8)Review maintenance task (‘C’ chk and ‘B’ chk) to inspect the cooling system and cleaning the E&E from dust and dirt.